A rotation speed sensor can be detachably mounted to an outer member of a wheel
bearing assembly. A sensor holder is a leaf spring folded in two and has upper
and lower portions having windows aligned with each other and a downwardly protruding
rib and an upwardly protruding rib, respectively, and a connecting portion. The
sensor is inserted through these windows until a rib formed on the connecting portion
engages in a groove formed in the back of the sensor. The holder is mounted on
the outer member until the downwardly protruding rib and upwardly protruding rib
engage in grooves formed in a ledge axially protruding from one end of the outer
ring and the sensor is received in a cutout formed in the ledge. In this state,
the holder is strained, thereby elastically holding the sensor in the cutout formed
in the ledge.
